One item that may not be addressed in the schematic is that the pipe must slope downward. The slightest upward grade or rise to clear another pipe, and the system will not work. A perfectly level pipe will allow the system to function, but at a greatly reduced efficiency.When you pipe a convection system, you have to pipe it as if it were a drainage system in order for it work properly, if at all.

: I looked at another house done by my plumber, and he did a hot water convection return loop as follows. The supply lines to upstairs are 3/4". He rean a 1/2" return line down to the water heater. He then added a connection to the hot water heater drain spigot and another spigot with a tee and tied the return line into the tee. Questions: is this "kosher" to use the drain line for this purpose? I see no one-way valve in the return line, this seems very important so that when hot water is used, you don't get sediment from the drain line sucked up through the return line.